As is fully explained in the U.S. Patent to Smith, No. 3,695,091, dated Oct. 3, 1972, shot peening the surface of a workpiece beyond "saturation" (overpeening) produces no beneficial results and is wasteful use of peening material and apparatuses. To achieve peening "saturation" and to avoid peening beyond the "saturation" point or overpeening, as well as achieving the correct degree of peening, means have been devised for the nondestructive measuring of peening intensity. One such device is the Almen strip which consists of a thin flat strip of the A, C or N type and having a size 7.62 centimeters (3 inches) long, 1.9 cm (3/4 of an inch) wide and a thickness of about 0.78 mm (0.031 inch) to about 2.38 mm (0.0938 inch). Another device for measuring the peening intensity of the surfaces of small diameter holes and which utilizes the Almen strip, is disclosed in the aforesaid Smith patent. In both these methods and devices the strip is subjected to shot peening for a specified time with the same combination of size of shot, material of the shot, and striking velocity of the shot as is to be used in the peening of workpieces such as a structural or machine part. After exposure of the strip to the shot, the amount of deformation or curvature of the strip is measured, and this curvature resulting from the impaction of peening shot constitutes a measure of the intensity of the stresses set up in the peened surface (or the extent of the compressive layer produced in the metallic surface) and hence, is a measure of peening intensity. The Almen test provides a means of measuring the results of a peening operation and, therefore, after several such tests and the recording of the exposure times, serves as a basis for establishing the treatment time for a particular workpiece.
It has been found that the Almen test strip, while satisfactory for relatively large exposed surfaces, is unsatisfactory for the measurement of peening intensity in small areas which may also be difficult to reach with the "rain" of shot.
It is therefore an object of the present invention to provide a method of and apparatus for measuring intensity of peening on small area surfaces in terms of the Almen scale.
It is another object of this invention to provide a method and apparatus for measuring peening intensity which is cheaper and more reliable than the use of Almen strips.